The legal interpretation of a three-letter word could sink the results of countless alcohol breath tests in drunken driving cases across Missouri.

The St. Louis Post-Dispatch reported Thursday that several St. Charles County defense lawyers have successfully challenged blood-alcohol level test results over a linguistic error that remained in state regulations for 14 months before it was fixed in late January.

State Department of Health and Senior regulations say the breath-test machines must be periodically tested by police at one of three blood-alcohol levels: 0.10 percent, 0.08 percent or 0.04 percent. Before the fix, the rules included the word "and" rather than "or." Some defense attorneys successfully argued that police had to conduct tests at each of those three levels. The legal limit for blood-alcohol levels for Missouri drivers is 0.08 percent.

In civil hearings last week, Associate Circuit Judge Matthew Thornhill ruled in favor of two alleged drunken drivers because officials couldn't prove breath analysis equipment was properly maintained to this standard. In both cases the drivers were able to have the suspension of their drivers licenses lifted. A Department of Revenue attorney disagreed at the hearings.

"I may not like doing it, but if the law says it's got to be done — that this is what the standard is and they didn't meet it — then I have to do what the law says," Thornhill said in an interview. "We take an oath. It isn't up to me to rewrite the law."

The elimination of breath test evidence could not only make it harder for the Department of Revenue to revoke driving privileges in civil cases but also make it tougher for criminal prosecutors to prove drivers were drunk.

News of the apparent loophole is spreading. Since Thornhill rendered the two judgments, eight more civil cases were argued in his court on the same basis. Decisions in those cases are pending.

"People are going to pick up on it all over the state because it's real," the judge said. "It's sitting right there in the regulations."

Officials with the Department of Health and Senior Services and the state Department of Revenue did not immediately respond to questions about the change in wording, St. Charles County Assistant Prosecuting Attorney John Bauer said was perhaps a clerical error.